In recent years the electroplating industry has been paying increasing attention to the discharge of undesirable elements into the environment. Pollution of streams by discharge of rinse water and air pollution by discharge of fumes from hot electroplating baths have been of particular concern. Such loss of pollutants from a plating plant also has a direct bearing on the economics of plant operation because the pollutants include chemical values the loss of which must be made up by additions to the plating tank.
A traditional way of handling the pollution problem has been to use relatively large quantities of water to dilute the pollutant. This adds to the economic problem and has doubtful value in pollution control. Recently the art has turned in the direction of what appears to be the only logical solution to the problem; that is, to make the plating operation as nearly as possible a closed ecological system.
An attempt toward a closed system is described, by way of example, by Withrow in U.S. Pat. No. 3,661,732. The latter patent describes by way of example, (a) the removal of 2000 gallons per minute of chromium bath liquid at 110.degree. F., (b) the removal of 30 gallons per minute of rinse water at 150.degree. F, (c) the joining of the two streams at 113.degree. F, (d) their transfer to a reservoir at 110.degree. F, (e) the heating of the liquid to 125.degree. F, (f) the passing of the liquid downwardly through a packed column countercurrent to air (35,000 cubic feet per minute collected in fume hoods over the plating baths plus 30,000 cubic feet per minute of auxiliary air), (g) wherein the air removes water from the liquid stream, and (h) wherein the liquid stream removes chemical values from the air. The resulting liquid stream, with less water and increased chemical values, is returned to the chromium plating bath.
It is the object of this invention to use such a closed system but in a much improved manner requiring (a) no added heat other than the waste heat generated in the plating baths, (b) much less added water in the rinse and (c) circulation of the heating of only a relatively small percentage of liquid for purposes of the water-chemical value interchange in the air scrubbing step.
It is a specific object of the invention to provide a preferred embodiment in which (a) the waste heat generated in the plating bath is the only heat used in water removal, (b) no water is circulated from the plating bath, (c) water added to the rinse is restricted by using a relatively low volume-relatively high pressure spray rinse, and (d) no auxiliary air is needed other than that required to sweep over the plating baths.